The invention relates to directional boring and, in particular to a system for boring through both soil, soft rock and hard rock using the same machine and specific assemblies for use in such a system.
At present, when underground utilities such as natural gas, potable water, or sanitary sewer pipes are placed in rock, trenches are excavated using large hard rock trenching equipment such as the Vermeer T-655, or possibly even shot using explosives. In these conditions, electric, telephone and cable TV lines are normally strung overhead along poles, mostly due to the difficulty and expense of placing them underground. Thus, in many situations, a solid rock formation will cause utility lines to be located above ground due to the difficulty of underground installation. Many such sites involve mixed conditions involving both a solid rock formation for part of the run and soil for the remainder, often at the beginning and end of the run. In such a situation, rock drilling or trenching equipment may lack the capability to bore through the soil to reach the rock formation.
Directional boring apparatus for making holes through soil are well known. The directional borer generally includes a series of drill rods joined end to end to form a drill string. The drill string is pushed or pulled though the soil by means of a powerful hydraulic device such as a hydraulic cylinder. See Malzahn, U.S. Pat. Nos. 4,945,999 and 5,070,848, and Cherrington, U.S. Pat. No. 4,697,775 (RE 33,793). The drill string may be pushed and rotated and the same time as described in Dunn, U.S. Pat. No. 4,953,633 and Deken, et al., U.S. Pat. No. 5,242,026. A spade, bit or head configured for boring is disposed at the end of the drill string and may include an ejection nozzle for water to assist in boring.
In one variation of the traditional boring system, a series of drill string rods are used in combination with a percussion tool mounted at the end of the series of rods. The rods can supply a steady pushing force to the impact and the interior of the rods can be used to supply the pneumatic borer with compressed air. See McDonald et al. U.S. Pat. No. 4,694,913. This system has, however, found limited application commercially, perhaps because the drill string tends to buckle when used for pushing if the bore hole is substantially wider than the diameter of the drill string.
Accurate directional boring necessarily requires information regarding the orientation and depth of a cutting or boring tool, which almost inevitably requires that a sensor and transmitting device (xe2x80x9csondexe2x80x9d) be attached to the cutting tool to prevent mis-boring and re-boring. One such device is described in U.S. Pat. No. 5,633,589, the disclosure of which is incorporated herein for all purposes. Baker U.S. Pat. No. 4,867,255 illustrates a steerable directional boring tool utilizing a pneumatic impactor.
Directional boring tools with rock drilling capability are described in Runquist U.S. Pat. No. 5,778,991 and in Cox European Patent Applications Nos. EP 857 852 A2 and EP 857 853 A2. However, although directional boring tools for both rock drilling and soil penetration are known, no prior art device has provided these capabilities in a single machine together with the ability to steer the tool in soil, soft rock and hard rock. Hard rock for purposes of the present invention means rock formations having a compressive strength of 18,000 psi or greater. Concrete typically has a compressive strength of around 8,000 and would be considered xe2x80x9csoft rockxe2x80x9d for this purpose, whereas granite may have a compressive strength of up to 80,000 psi. The present invention addresses this need.
U.S. Provisional Patent Application No. 60/122,593, filed Mar. 3, 1999 by a different inventive entity of which the present inventors are joint inventors, describes a drill head for an apparatus for directional boring including a starter rod, a holder for a device for detecting angular orientation such as a sonde, a pneumatic hammer and a rotary bit assembly connected head to tail with the starter rod at one end and the bit at the other. The bit has a frontwardly facing main cutting surface with a plurality of cutting teeth disposed thereon and a gage tower radially outwardly offset from the main cutting surface having at least one frontwardly facing gage cutting tooth thereon suitable for cutting over an angle defined by less than a full rotation of the bit. The device for detecting angular orientation is in a predetermined alignment with the gage tower so that it determines the orientation of the gage tower relative to the axis of rotation of the drill head. In one preferred embodiment, the main cutting surface is substantially flat and circular and has a series of fluid ejection ports thereon, and the drill head has passages for conducting a drill fluid therethrough to the ejection ports. In another preferred embodiment, the bit has a heel portion on an outer side surface thereof at a position opposite the gage tower, which heel portion slopes inwardly from back to front.
Such a drill head may be used in a method for directional boring using a directional boring machine which can push and rotate a drill string having the drill head mounted thereon. Such a method comprises the steps of boring straight through a medium by pushing and rotating the drill head with the drill string while delivering impacts to the bit with the hammer, prior to changing the boring direction, determining the angular orientation of the gage tower using the device for detecting angular orientation, and changing direction during boring by pushing and rotating the bit repeatedly over an angle defined by less than a full rotation of the bit while delivering impacts to the bit with the hammer, so that the drill head deviates in the direction of the cutting action of the gage tower. The medium may be soil, solid rock, or both at different times during the bore. In particular, the steps of boring straight and changing direction can be carried out in both soil and rock during the same boring run using the same bit.
According to a further aspect of the foregoing application, a method is provided for directional boring in mixed conditions including both soil and solid rock. Such a method includes the steps of boring straight in both soil and rock by pushing and rotating the drill head with the drill string while delivering impacts to the bit with the hammer, prior to changing the boring direction in both soil and rock, determining the angular orientation of the gage tower using the device for detecting angular orientation, changing direction when boring in rock by pushing and rotating the bit repeatedly over an angle defined by less than a full rotation of the bit while delivering impacts to the bit with the hammer, so that the drill head deviates in the direction of the cutting action of the gage tower, and changing direction when boring in soil by pushing the bit with the drill string without rotating it so that the drill head deviates in a direction of the gage tower and away from the heel portion. Since the main cutting face of the drill bit is large and flat, the pushing force of the drill string alone may be insufficient to steer the tool in soft ground without rotation. It is thus preferred to deliver impacts to the bit with the hammer while changing direction in soil. This method may provide better steering in some ground conditions.
The present invention provides a number of specific mechanical improvements to a drill head for carrying out the method of the foregoing provisional application. According to one aspect of the present invention, the bit has a gage tower oriented to the clock position of the sonde. This is done through a series of master splines or keyways that align the planes. The joints include sonde housing to body, body to front bushing, front bushing to bit shaft and bit shaft to bit. This alignment is key to any percussive hammer, fluid or pneumatic actuated, in it guarantees correct positioning of the gage tower relative to the sonde so that steering can be carried out with accuracy.
According to a second aspect of the invention, the bit is externally removable from the bit shaft. Changing the bit does not require disassembly of the hammer as all other down hole hammers do. Roll pins retain the bit to the bit shaft and an optional drive key may be interposed between the bit and bit shaft.
According to a third aspect of the invention, a splined connection is used to attach the sonde housing to both the starter rod and the sonde housing attachment to the hammer. The hammer may thereby be removed from the sonde housing and a rock drill head may be installed in its place should soft rock be encountered.
According to a fourth aspect of the invention, the front end cap and splined sleeve of the tool are clamp loaded using bolts, making tool disassembly easy compared to existing hammers. The use of a threaded connection between the sleeve and the impactor housing is permitted, but a front end cap is mounted by keying splines onto the impactor. Over- or under-tightening of the sleeve is avoided because one or more bolt holes in the cap will not align properly with bolt holes in the sleeve unless the sleeve is in the correct position relative to the sonde as described hereafter.
According to additional aspects of the invention, the tool has a unique start-up and shut down mechanism. An air passage connects the forward pressure chamber of the hammer to atmosphere out of the bit when frontal (thrust) pressure is removed, and a unique valving mechanism is provided which starts up when a predetermined forward thrust is exerted on the drill head by the drill string. The hammer expels air leaking past the striker to the rear chamber through clearance in the spline joint between the sonde housing and hammer, and the main valve is not secured to the hammer in any way. It floats in the recess at the front of the splined joint between sonde housing and hammer. The valve becomes trapped when the joint is pinned together.
According to a further aspect of the invention, the mass centroid of the hammer and sonde housing assembly is offset from the lengthwise axis of the head in a direction opposite to the direction the gage tower extends. Such an off center mass enhances the desired deflection of the hammer, thereby increasing the maximum rate of steer that can be achieved. The center of mass of the drill head can be most readily adjusted by offsetting the sonde housing and optionally the starter rod away from the gage tower to shift the center of mass of drill head in a favorable direction. The invention further contemplates an improved sonde housing which takes advantage of such offset to provide an improved air supply to the hammer.
A preferred form of fluid-powered impactor according to the invention for use in a drill head including a bit includes a tubular housing, a valve stem seated in the housing for receiving a supply of compressed fluid, the valve stem including a lengthwise passage ending in at least one radial port and a reduced diameter front end portion of the valve which extends forwardly from the radial port, a striker disposed for sliding movement within the housing, wherein a rear end opening in the striker receives the reduced diameter front end portion of the valve and forms a rear pressure chamber that receives pressure fluid from the port of the valve stem and exerts a force effective for propelling the striker forwardly, and a bit shaft slidably mounted in a bit shaft support assembly for movement between an extended position and a retracted position, which bit shaft has a front end on which the bit of the drill head is mounted in use, whereby separation between the housing and bit decreases as the bit shaft moves from its extended to its retracted position. Passages in the striker and valve stem configured so that: (i) when the bit shaft is in its extended position and the striker is in contact with a rear impact surface of the bit shaft, an air flow path is formed which permits compressed air from the rear pressure chamber to exhaust to the atmosphere; (ii) when the bit shaft is in its retracted position and the striker is in contact with a rear impact surface of the bit shaft, an air flow path is formed which permits compressed air from the rear pressure chamber to flow into a front pressure chamber ahead of the striker and thereby cause the striker to move rearwardly; and (iii) when the bit shaft is in its retracted position and the striker is moving rearwardly, the front pressure chamber exhausts to the atmosphere and pressure in the rear pressure chamber causes the striker to reverse direction and deliver a forward impact to the bit shaft. Operation of the hammer occurs in (ii) when a rearward pushing force exerted on the housing while the bit shaft is held from forward movement is sufficient to cause the bit shaft to assume its retracted position against the force exerted in the rear pressure chamber. The bit shaft preferably has a lengthwise bore through which exhaust can flow to the front end of the bit shaft and hence out through passages in the bit.
A drill head for an apparatus for directional boring according to another aspect of the invention includes a bit configured for directional boring, which bit can be steered by cutting over a limited arc of rotation with a predetermined cutting surface of the bit, a holder for a device for detecting angular orientation of the bit, including a key that permits mounting of the device in a predetermined position, a hammer positioned to deliver impacts to the bit, wherein the hammer, holder and bit are connected in series head to tail to form the drill head, and a connection suitable for mounting the drill head to a drill string, e.g., threads or a splined connection as described hereafter. A series of keying connections between the holder, hammer and bit key the angular orientation of the cutting surface of the bit to the angular orientation of the key of the holder, such that each connection fits together only when its angular orientation is keyed to (in a predetermined alignment with) the key of the holder. Preferably the keying connections comprise a plurality of spline and groove connections between each of the components.
The invention further provides a tubular housing configured for use in a drill head for an apparatus for directional boring for housing a device such as an impactor. The housing has a front end portion configured to form a first keying connection at a front end thereof and a second end portion configured to form a first keying connection at a rear end thereof. The first and second keying connections comprise a plurality of longitudinal spline and groove connections, such that the housing has one or the other (splines or grooves) at each end for coupling with adjacent drill head components.
A rock drilling bit assembly according to the invention includes a drill bit including a bit body, a front drilling surface having a plurality of cutting teeth extending therefrom, a rearwardly opening recess, and a transverse hole intersecting the rearwardly opening recess, and a bit shaft having a front end portion configured for a close fit into the recess of the drill bit and having an outwardly opening transverse groove which comes into alignment with the transverse hole in the drill bit for receiving a retainer therein. As noted below, such a bit may be interchanged as needed with a soil bit lacking teeth suited for rock drilling but with a sloped front face suitable for rapid steering in soil. In a preferred embodiment, the bit shaft has an enlarged diameter rear portion configured for sliding, sealing engagement inside of a tubular sleeve or tool housing and a series of external, longitudinal splines thereon ahead of the rear portion and configured for sliding engagement with grooves in the member (sleeve or tool housing) in which the bit shaft is mounted. For keying purposes, one of the bit shaft splines is preferably a master spline having a different size (such as circumferential width) that at least one other spline.
A drill head for an apparatus for directional boring according to another aspect of the invention includes a bit configured for directional boring, which bit can be steered by cutting over a limited arc of rotation with a predetermined cutting surface of the bit, a holder for a device for detecting angular orientation of the bit, including a key that permits mounting of the device in a predetermined position, a hammer positioned to deliver impacts to the bit, wherein the hammer, holder and bit are connected in series head to tail to form the drill head, a connection suitable for mounting the drill head to a drill string, and a series of connections between the holder, hammer and bit which key the angular orientation of the predetermined cutting surface of the bit to the angular orientation of the key of the holder. The mass centroid of this drill bit is located on an opposite side of a lengthwise axis of the drill head from the predetermined cutting surface of the bit. Alternately, the mass centroid is on the opposite side from the predetermined cutting surface or gage tower of a plane bisecting the drill head in a widthwise direction and passing through its longitudinal axis. This placement provides better drilling action to the bit as explained below.
The invention further provides an improved sonde holder for use in a drill head including at least a bit, the sonde housing and a connection at a rear end of the drill bit for connecting the drill head to a drill string, with or without a starter rod or impactor. The sonde holder includes a cylindrical housing having front and rear end connecting portions configured for coupling the sonde holder into the drill head assembly, which front and rear connecting portions are in alignment with a longitudinal axis of the sonde housing which coincides with a longitudinal axis of the drill head. A flow passage is provided through the housing for passing compressed fluid from rear to front in the sonde holder, and a sonde compartment is provided therein suitable for containing a sonde in a keyed position, which compartment is isolated from the flow passage and laterally offset therefrom. The cylindrical housing including a portion thereof defining the sonde compartment projects laterally from the longitudinal axis of the sonde housing which coincides with the longitudinal axis of the drill head, whereby the mass centroid of the sonde holder is offset from the a longitudinal axis of the sonde housing which coincides with the longitudinal axis of the drill head. A removable cover may be provided for accessing the sonde compartment, which cover is laterally offset from the longitudinal axis of the sonde housing which coincides with the longitudinal axis of the drill head and thereby contributes to the offset of the mass centroid of the sonde holder.
The invention also provides a substitute bit for use in with the foregoing drill heads of the invention for use when more rapid boring through soil is desired. The soil bit comprises a bit body having a frontwardly facing sloped face that defines an acute included angle relative to a lengthwise axis of the bit and configured for steering the bit through dirt when a pushing force is applied to the bit without rotating the bit. The bit further has a rearwardly opening recess for mounting the bit onto a bit shaft, at least one transverse hole intersecting the rearwardly opening recess and configured for insertion of a retaining pin therein which can mechanically interlock the bit to the bit shaft, and a fluid passage configured to carry pressure fluid from the recess to a location away from a front end of the bit.
These and other aspects of the invention are described in the detail description that follows.